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Durham University

Department of Mathematical Sciences

Academic Staff

Publication details for Peter Craig

Barcelo Culleres, D, Black, R, Boesten, J, Boobis, A, Hardy, A, Hart, A, Koepp, H, Luttik, R, Machera, K, Maroni, M, McGregor, D, Meyer, O, Moretto, A, Papadopoulou-Mourkidou, E, Petzinger, E, Savolainen, K, Schaeffer, A, Stenström, J, Steurbaut, W, Tsipi-Stefanitsi, D, Vleminckx, C, Aldenberg, T, Craig, Peter, Forbes, V & Roelofs, W (2006). Opinion of the Scientific Panel on Plant health, Plant protection products and their Residues on a request from EFSA related to the assessment of the acute and chronic risk to aquatic organisms with regard to the possibility of lowering the uncertainty factor if additional species were tested. And Appendix: Mathematical and statistical basis of options for risk calculations (section 5 of the opinion). Parma, Italy, European Food Safety Authority.

Author(s) from Durham


The Scientific Panel on Plant Health, Plant Protection Products and their Residues (PPR Panel)
was asked by EFSA for an opinion on the possibility of refining the acute and chronic aquatic risk
assessment of pesticides by lowering the assessment factor if additional species were tested. In
particular, the PPR Panel was asked how these values could be reduced when additional singlespecies
studies are available whilst still maintaining the same level of protection as foreseen in
the Directive 91/414/EEC.
The current approach for acute and chronic risk assessment to protect the ecosystem against
adverse effects of pesticides uses the lowest available toxicity value from laboratory standard
toxicity tests, i.e. the most sensitive tested species, and divides this value by a fixed assessment
factor. This results in an increase of conservatism when more species are tested and does not
reflect the increased certainty that more data provide.
To answer this question the PPR Panel reviewed existing literature, guidance documents, and
data. Statistical calculations based on species sensitivity distributions were used to develop a
range of options for adjusting the risk assessment when more species are tested.
The PPR Panel assessed the current level of protection and found that it is not equal for
different taxonomic groups and for different substances. On average, the level of protection
provided by the current approach is, for example, markedly higher for fish than for crustaceans
and insects. The PPR Panel identified a range of possible methods either to maintain at least
the current unspecified level of protection, or to achieve any specified level of protection.
For taxonomic groups where the legislation requires only one species (e.g. crustaceans), this
effectively sets the level of protection in the effects assessment. When additional species are
tested, the same average level of protection can be maintained by taking the geometric mean
(rather than the lowest value) and dividing by the current assessment factor.
For fish, where the legislation requires that at least two species are tested, this implies a higher
level of protection in the effects assessment. In this case, a different procedure is required when
additional species are tested. The minimum is then replaced by the second or third lowest
toxicity value depending on the sample size available, and divided by the current assessment
The Panel described three further approaches that allow a particular level of protection to be
achieved, provided such a level is specified. These methods involve using a modified
assessment factor that incorporates an estimate of the variation between species, which can
either be specific to the substance under consideration or derived from existing information on
related substances. These three methods relate only to uncertainty due to variation between species. Any other uncertainties that are relevant to the assessment would need to be
accounted for separately.